This application pertains to the art of indicators and, more particularly, to indicators for indicating overtravel of a piston. The invention is particularly applicable for use in a pressure converter for converting pneumatic pressure to hydraulic pressure. However, it will be appreciated that the invention has other aspects and may be used with other cylinders or other devices which overtravel.
Piston overtravel indicators of a known type include that disclosed in U.S. Pat. No. 3,997,887 issued Dec. 14, 1976, to Poynter. In this indicator arrangement, an elongated indicator rod extends slidably through a cylinder end wall toward which a piston moves. The indicator rod has an inwardly extending armed position and is engageable by the piston upon overtravel thereof toward the end wall for movement to an outwardly extended operated position. An independent switch assembly is mounted to the end wall and has a plunger engageable with the indicator rod for operating the switch when the rod is moved to its operated position. An indicator assembly of the type described is relatively expensive to manufacture and assemble, and requires maintenance in the event the switch assembly fails.
In another known arrangement, a separate switch assembly is not used and an electrical circuit is completed when the piston engages the indicator rod. However, once the piston moves back from a slight overtravel position, the electric circuit is again opened. Momentary operation of the overtravel indicator in this manner can result in a failure of an operator to see or hear the indicator. It would be desirable to have an arrangement wherein a separate switch assembly was not required, and wherein the indicator would remain on once it was operated even though the piston is retracted from an overtravel position.